The present invention relates to a rate conversion digital filter in which the sampling rate of the input digital signal is reduced by a factor of 1/2. The present invention is particularly useful for digital recording of two-channel signals.
Sampling rate reduction techniques are used for interfacing different types of digital communications media which proliferate at an increasing rate in various fields of application. In digital audio techniques, for example, original analog signals are sampled at a predetermined sampling frequency fs and quantized into a digital stream of 16-bit words. If the original signal has a bandwidth exceeding the fs/2 limit, foldover distortion, or "aliasing" occurs. For this purpose the analog signal is passed through an analog low-pass filter having a cut-off frequency of fs/2 before it is sampled. Since audio recording requires a distortion factor as high as 70 to 80 dB, the roll-off characteristic of the filter must be as sharp as possible and group delays resulting from such filter characteristic must be equalized.